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Unequal karat


#1

I would like to see some discussion on why a 14k ring cast in a
centrifuge will test higher (appx. 18k) on top and lower (appx.
10k) at the shank. There are two schools of thought on this at our
store. Since I fall into one camp I do not wish to prejudice the
discussion by offering more at this time. Although
the example given was for 14k, we are as interested in how this
would apply to 18k gold ( and here we are again divided as to
whether the higher karat makes a difference).


#2

About the ring of varying karatage- It would seem to me that
possibly when the gold was alloyed it was not stirred or that they
dumped alloy, pure, and all into the casting machine without mixing
the alloy and heating seperately and then casting, but thats just
my humble opinion. If the gold was not alloyed prior and was
alloyed in the casting machine and not mixed homogenously, you
know, theory says that the heaviest componet will end up at the
bottom of the flask first. I wonder if anything else lower on the
tree was of a higher karatage than the 18K? This is why we use an
electromelt first, and then pour into the crucible for the caster.
About what might be outcome of an assay I won’t speculate on- What
do you say, J.A.? Rick in Houston


#3

Rick,

I was told that the customers lawyer had the 14K ring I mentioned
fire assayed (13.9K), which was enough to forestall a lawsuit. My
contention is that this was one of those times that the caster
mixed the gold in the crucible during the casting run.

The caster states that as long as he mixes well in the crucible
that there is no difference between mixing karat alloy during the
casting run and using a premixed karat alloy. Furthermore, because
we are using a centrifuge that the heavier gold will tend to
separate from the other metals regardless of how homogenous the
alloy may be, and that this action also applies (to a lesser
degree),to vacumn casting due to the force of gravity. He also
maintains that premixing 18K prior to the casting run is
detrimental to 18K in particular because of the extra melt.

Now, let’s set aside considerations like overheating the gold. A
large proportion of our work is in 18K. Most of my casting
experience is with 14K, but I do maintain that for the purposes
under discussion that karat makes no difference, that because an
alloy is a compound that the metals cannot be separated by
physical force. Therefore when this problem occurs we are dealing
with an incomplete mix of either alloys or the elemental metals
themselves. (I must admit I’m a little weak here. We are getting
into areas a bit over my head.)

I must end by saying that we are both experienced jewelers, and
firm believers in quality. Each of us is sure of our position, and
we would like to resolve this problem. We are also wondering what
we have overlooked.

Tom